JP2002532036A - Queue management in packet-switched networks. - Google Patents

Abstract

(57) [Summary] In a multipoint-to-point link, a packet (T) is transmitted to a central node (10) via a shared medium in response to a grant (TP). The central node (10) issues a grant to the multipoint node (20) based on the queue size record (11) held at the central node. The queue record is updated when a queue size report (grant request) (RP) is received from the multipoint node. Wrong queue values may be recorded at the central node when grants and grant requests are sent almost simultaneously due to transmission delays across the link. If the central node keeps a record of the grant sent during the preceding round trip delay, this problem is overcome and the forwarding capability is improved. All incoming permission requests are adjusted by the number of stored permissions before being used to update the queue record.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001] The present invention relates to media access control (MAC) in packet-switched networks. In particular, the invention is directed to managing the forwarding of packets between one of several multipoint nodes and a central node.

BACKGROUND ART [0002] Point-to-multipoint links (point-to-multipoint links) in packet-switched networks
-multipoint link) media access control means that any one of a plurality of nodes on the multipoint side of the link transmits, via a shared medium, a packet to one central node located at the other end of the link. Is a mechanism that determines whether or not it can be sent. In conventional media access control mechanisms used in bi-directional TDMA transfer links, the central node adds grant information, commonly referred to as grant, to every packet it sends. This permission is addressed to one of the multipoint nodes and specifies which time slots of the future packet stream are available to that addressed multipoint node to send the packet. .

[0003] Permissions are assigned in response to requests. Multipoint nodes typically send requests in the form of queue size information when packets are present at the node and waiting for transmission. The central node sends the corresponding permits and requests for permits more frequently than it can send the permits.
Manages priority assignment when arrives. To this end, each multipoint node is provided with a queue that stores packets until the node is authorized to forward the packet.

[0004] Each multipoint node keeps track of the number of packets queued and waiting for transmission, and a corresponding grant request is sent to the central node. The central node is
Maintain a queue length record at each multipoint node. The central node issues a grant to the multipoint node requesting channel capacity based on the records in this queue.

[0005] The central node's queue record is updated with queue information in the form of an authorization request received from the multipoint node. This request represents the current queue size at the multipoint node and is used to overwrite the recorded queue size at the central node. The recorded queue size at the central node is reduced each time permission to send a packet to the corresponding multipoint node is sent.

[0006] Information transfer between the central node and the multipoint node includes a delay,
This delay depends on the available bandwidth and the length of the transfer medium. There is also a delay at the multipoint node when processing grants received from the central node. Thus, there is a window during which the multipoint node sends a grant request and the central node sends a grant to the multipoint node based on the queue record before receiving the grant request. . When the authorization request arrives at the central node, the queue record is overwritten by the wrong queue size value. This error does not cause the packet to be lost, but will send more permissions than is actually required. The arrival of more packets at the multipoint node can alleviate the discrepancy between the actual queue size and the recorded queue size to some extent, but after all (on balance), the central node The probability of issuing an unavailable permit is high. Therefore, the channel capacity is wasted.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method and apparatus that alleviates the problems of the prior art.

It is another object of the present invention to provide a method and apparatus that significantly improves the utilization of the channel capacity of a multipoint-to-point link.

The purpose of this is to allow the traffic receiving node, which keeps a queue record of the number of packets waiting to be forwarded at the traffic sending node, to determine the number of grants during a given delay after transmission of each grant, This is accomplished by storing the equivalent number of packet transfers enabled by the grant and modifying the value of the incoming grant request by the number of stored grants. This delay preferably corresponds to the round trip delay between the two nodes in question. This is the sum of the delay in granting and the delay in reporting. That is, the sum of the time between the grant sent by the traffic receiving node and the traffic packet sent by the traffic sending node. This delay also includes the processing delay required by the traffic sending node to recognize the grant, ie process the grant.

[0010] The invention also resides in a node of a communication network receiving traffic from at least one further node via a shared medium. The node stores the number of grants sent to this further node during a predetermined delay after transmission of each grant, i.e., the equivalent number of packet transfers enabled by these grants. Is configured to modify the incoming queue size report from the stored permission value.

[0011] It is further proposed a communication network comprising a central node and several multipoint nodes, wherein the multipoint nodes are connected to said central node by a shared medium. The central node keeps a record of the queue size for each multipoint node and the number of grants sent to each multipoint node during a given delay, i.e., the equivalent packet that became operational. Means for storing the number of transfers and modifying the incoming queue size record corresponding to the multipoint node in question.

Storing the number of grants sent during the preceding round trip delay effectively determines the number of grants that have not yet been processed and responded to at the corresponding multipoint node. Queue size records or grant requests received from the corresponding multipoint node during this time will be issued without knowledge of the grant. Using the number of grants sent, or, if more than one packet could be sent with one grant, using the equivalent number of packets enabled
By modifying the value in this record, the reported queue size is corrected and the correct value is used to overwrite the central node's queue record.

By means of the method according to the invention and the devices of the nodes and the communication network, the queue size record of the traffic receiving node is constantly adjusted to reflect the actual number of required grants. Thus, the conventional overestimation of the queue size and the resulting allocation of unused time slots is eliminated. As a result, the transfer capacity and efficiency of the communication network are improved.

DETAILED DESCRIPTION OF THE DRAWINGS In the drawings, like reference numbers are used for the same or identical components.

A representative multipoint-to-point link of a TDMA packet-switched communication network is shown in FIG. Several multipoint nodes 20, three of which are shown, communicate with the central node 10 via one shared, bidirectional channel. Channel 100 may be a fixed electrical or electro-optical link or an air interface.

A media access control (MAC) mechanism is a centralized device that determines which multipoint node of the plurality of multipoint nodes uses which time slot of the shared channel 100 to transmit a packet. Used by node 10. Here, it is assumed that a packet is an amount of information that can be transmitted via the channel 100 in one time slot. Depending on the service using this channel, a packet may include one or several frames, or parts of frames.

A conventional media access control procedure is shown in FIGS. 2a to 2k. FIG.
2a through 2k illustrate the central node 10 of the link shown in FIG.
2 shows a very simplified diagram of the flow of frames or packets between nodes 20. Each frame is sent in one time slot 30. 2a to 2k, the downlink is shown above and the uplink is shown below. The dotted line represents the interface between the channel 100 and each of the nodes 10,20.

In the illustrated link, the transmission delay, ie the passage of time between two nodes, is equal to the time of three slots. Assume that the processing time of the multipoint node is equal to one slot time 30. This is represented by the time slot 31 of the multipoint node 20. Each successive figure is time slot 1
Represents links at intervals.

FIG. 2 a shows the starting state, in which the multipoint node has a queue length of six packets waiting to be transmitted, and the central node 10 determines the length of this queue. Record 11 is held. Central node 10 has just sent a permit to send a request RP to multipoint node 20. The permission RP to send the request is a traffic permit T
Via request Rn of P, there is an invitation to the multipoint node 20 to indicate the number n of grants required to send all the packets in the queue. Thus, the authorization request Rn is actually a report of the queue size. One grant in the example shown represents one time slot, and this time slot 1
Packets can be sent in pieces. However, it will be appreciated that the grant may represent, for example, an invitation to send more than one packet in successive time slots. Turning to FIG. 2b, it can be seen that the granting RP sending the request has been advanced on the link by one time slot delay, and the central node 10 has been followed by sending the first traffic granting TP. I can do it. The issuance of this traffic permit TP by the central node 10 has reduced the recorded queue length 11 by "1". However, the actual queue of the multipoint node is still "
6 ". This is because no packets have been sent yet.

In FIG. 2c, another traffic grant TP has been issued by the central node 10 and the recorded queue length has been modified to “4”. The granting RP to send the request is still sending. In FIG. 2d, the granting RP sending the request is a multipoint
Arrived at node 20 and processed. As explained above, this takes one slot represented by slot 31. During this time, the central node 10 has issued a third traffic grant TP, and the recorded queue size 11 has been reduced to "3". In FIG. 2e, when the permission RP to send the request is processed by the multipoint node 20, the request is to send six traffic permission TPs. The first traffic permitting TP arrives at the multipoint nodes 20, 31 and is ready to be processed. At the same time, the central node issued a fourth traffic grant TP and modified the recorded queue size to "2".

In FIG. 2f, the multipoint node 20 has processed the first traffic grant TP and has transmitted a first response traffic packet. Multipoint node 2
A queue of 0 will contain 5 packets. When the central node issues the fifth traffic grant TP, the queue size 11 has been modified to "1". The records in the queue in FIG. 2g eventually decrease to zero as the sixth final traffic grant TP is sent. Since the multipoint node 20 has responded to the second traffic grant TP by sending a second packet, the actual queue size at the node 20 is reduced to "4". In FIG. 2h, the central node is:
A permission request R6 for overwriting record 11 in the queue is received. Therefore, the record 11 in the queue is updated to “6”. During this time, the multipoint node 20 continues to send packets in response to the grant. This operation continues from FIG. 2i to FIG. 2k until all packets of multipoint node 20 have been sent in response to the sixth grant. Therefore, the final queue of the multipoint node 20 will be zero. However, the recorded queue size 11 at the central node 10
Is "6".

In this particular example, the queue size error recorded at the central node 10 is a request for traffic perm transmitted on the downlink.
its) Rn, these grants being transmitted on the uplink during the same time. Both nodes issue information efficiently without knowing the information being transmitted.

FIGS. 3 a to 3 l show a procedure for eliminating this error source according to the invention. The central node 10 in this arrangement includes a permission memory 12 for recording the number of traffic permission TPs transmitted within a predetermined time after transmitting the traffic permission TP. Any temporary storage medium, such as a counter, may be used. This memory 12 efficiently stores the history of traffic-permitted TPs issued to the multipoint node 20 during the preceding round trip delay. In the present invention, this means that the register 12 is adapted to hold the number of grants sent in the time of the preceding seven slots. These slots 7
This time corresponds to the round trip delay between the central node 10 and the multipoint node 20. Specifically, this delay is due to the time required for the traffic grant TP to arrive at the multipoint node 31 and be processed there, and the traffic packets T sent by the multipoint Equal to the time plus the transmission delay to arrive at 10.

For the procedures of FIGS. 2a to 2k, it is assumed that the delay in processing the authorization request Rn, ie, the update of the queue size recorded at the central node, is negligible. Hereinafter, this procedure according to the present invention will be described with reference to FIGS. 3a to 3k. These figures show the same sequence of events as shown in FIGS. 2a to 2k for an arrangement according to the invention. FIG. 31 shows the delay of three time slots of the link after FIG. 3k.

In FIG. 3 a, six packets are waiting in the queue of the multipoint node 20. The central node 10 keeps a record 11 of this queue size,
You have just issued a permission RP to send the request. Since no traffic permission TP has been sent during the preceding seven slots, the memory 12 is empty.

In FIG. 3b, a first traffic grant TP is transmitted following the grant RP sending the request. This event causes record 11 in the queue to decrement by "1". The memory 12 increments and holds the value “1”.

During the following time slot 30 (FIGS. 3c to 3e), three more traffic permitting TPs are issued. Therefore, record 11 of the resulting queue
Is “2”, and the value in the permission memory 12 is “4”. During this time, the multipoint node 20 issues a response to the RP in the form of six grants R6. This response R6 is
While traveling towards the central node 10, two more traffic grant TPs are issued (FIGS. 3f and 3g), reducing the queue record 11 to zero and setting the value of the grant memory to "6". . At the end of this time slot, six grant requests R6 have arrived at the central node 10 and this is illustrated in FIG. 3h, which shows the status of the subsequent time slot. It will be recalled that the processing time at the central node is considered negligible. However, before the permission request R6 is used to overwrite the queue record, the value of the queue record is first adjusted by the number of permissions stored in the permission memory 12. Since the first grant was sent seven time slots ago, six grants are stored in memory. The stored permission is subtracted from the request value R6, and the request value becomes zero. This value is used to update or overwrite the recorded queue value 11. Thus, the recorded queue value 11 remains in fact unchanged. As shown in FIG. 3i, in the next slot period, the round trip delay of seven time slots with respect to the first traffic grant TP expires. Therefore,
The permission memory is decremented by "1". In FIGS. 3j and 3k, as the delay of three or more traffic permitting TPs expires, the permitting memory 12 is further reduced. Finally, FIG. 31 shows the continuation of the delay of three time slots,
After the last permission delay, the permission memory 12 is finally set to zero.

It will be appreciated that the time during which the authorization memory 12 actually stores the authorization record exceeds seven time slots. This is because it is inevitable that there will be some finite processing delay associated with the central node 10.

As a result of adjusting the queue size report (grant request), the recorded queue size 11 at the central node 10 always accurately represents the number of packets waiting to be transmitted at the multipoint node 20. ing.

In the case of the multipoint-to-point link shown in FIG.
Is the queue size record 1 at each of the multipoint nodes 20
1 are held individually. In addition, the central node stores the number of traffic grants issued during the preceding round trip delay for each multipoint node 20. It will be appreciated that various multipoint nodes may be associated with various round trip delays. Each grant memory 12 assigned to a particular multipoint node 20, or the grant memory portion of the memory assigned to a grant, is adapted to store a grant transmission history for the corresponding delay.

In order to eliminate the risk that the central node 10 will underestimate the number of packets waiting at the multipoint node 20, the period between recording the grants sent is the frame delay between the two nodes and , In view of the time obtained by adding the delay of one time slot, it must be shorter than the round trip delay. This prevents all grant requests Rn reporting newly arrived packets from being reduced or decremented by the number of misstored grants. In terms of the simplified model shown in FIGS. 2 and 3, the delay must be shorter than eight time slots,
There must be at least seven time slots.

Each multipoint node 20 may maintain more than one queue so that various packets waiting to be transmitted are assigned to various queues and processed with different priorities. Will be able to understand. The central node 10
The values of these different queues are kept in a queue record 11 assigned to the multipoint node. In this case, the number of grants issued for packets in the various queues is stored separately and this record is used to adjust the value of the corresponding queue size in the queue record.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing a multipoint-to-point link in a TDMA packet switching network.

2a is a diagram schematically illustrating a process conventionally used at a central node of the communication network of FIG. 1 to record the size of a packet queue located at a multipoint node.

2b is a diagram schematically illustrating a process conventionally used to record the size of a packet queue located at a multipoint node at the central node of the communication network of FIG. 1;

2c schematically illustrates a process conventionally used at the central node of the communication network of FIG. 1 to record the size of a packet queue located at a multipoint node.

FIG. 2d is a diagram schematically illustrating a process conventionally used at the central node of the communication network of FIG. 1 to record the size of a packet queue located at a multipoint node.

2e schematically illustrates a process conventionally used at the central node of the communication network of FIG. 1 to record the size of a packet queue located at a multipoint node.

2f schematically illustrates a process conventionally used at the central node of the communication network of FIG. 1 to record the size of a packet queue located at a multipoint node.

2g schematically illustrates the process conventionally used at the central node of the communication network of FIG. 1 to record the size of the packet queue located at the multipoint node.

2h is a diagram schematically illustrating a process conventionally used at the central node of the communication network of FIG. 1 to record the size of a packet queue located at a multipoint node.

FIG. 2i schematically illustrates a process conventionally used at the central node of the communication network of FIG. 1 to record the size of a packet queue located at a multipoint node.

2j is a diagram schematically illustrating a process conventionally used at the central node of the communication network of FIG. 1 to record the size of a packet queue located at a multipoint node.

2k schematically illustrates a process conventionally used at the central node of the communication network of FIG. 1 to record the size of a packet queue located at a multipoint node.

FIG. 3a is a diagram schematically illustrating a process of adjusting a queue record according to the present invention at the central node of the communication network of FIG. 1;

FIG. 3b is a diagram schematically illustrating a process of adjusting queue records according to the present invention at the central node of the communication network of FIG. 1;

FIG. 3c is a diagram schematically showing a process of adjusting queue records according to the present invention at the central node of the communication network of FIG. 1;

FIG. 3d is a diagram schematically illustrating processing for adjusting queue records according to the present invention at the central node of the communication network of FIG. 1;

FIG. 3e is a diagram schematically illustrating a process of adjusting a queue record according to the present invention at the central node of the communication network of FIG. 1;

FIG. 3f is a diagram schematically illustrating processing for adjusting a queue record according to the present invention at the central node of the communication network of FIG. 1;

FIG. 3g is a diagram schematically showing a process of adjusting queue records according to the present invention at the central node of the communication network of FIG. 1;

FIG. 3h is a diagram schematically showing processing of adjusting queue records according to the present invention at the central node of the communication network of FIG. 1;

FIG. 3i is a diagram schematically showing a process of adjusting a queue record according to the present invention at the central node of the communication network of FIG. 1;

FIG. 3j is a diagram schematically illustrating a process of adjusting queue records according to the present invention at the central node of the communication network of FIG. 1;

FIG. 3k is a diagram schematically illustrating a process of adjusting a queue record according to the present invention at the central node of the communication network of FIG. 1;

FIG. 31 is a diagram schematically showing processing of adjusting queue records according to the present invention at the central node of the communication network of FIG. 1;

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Claims (14)

[Claims] 1. A method for a first node (10) of a communication network managing the transfer of information of a packet (T) from a second node (20) via a channel (100), the method comprising: Holding a queue record (11) representing the number of packets waiting to be transmitted at the second node (20), and receiving a queue size value (Rn) from the second node; Updating the record (11) of the channel (100) on the channel (100) to the second node (20) during a predetermined time after the issuance of each grant (TP). Record the issuance of a slot assignment permit (TP) and update the queue size value (Rn) received from the second node (20) before updating the queue record (11), Depending on the number of permissions recorded, Wherein the adjusting. 2. The method according to claim 1, wherein the time is a predetermined time. 3. The method according to claim 1, wherein the time is equal to a round-trip transmission delay between the first and second nodes (10, 20). . 4. The method according to claim 1, wherein the time is determined by the first node (10) sending a grant and the second node receiving the grant. And the delay between the second node (20) sending packets in response to the grant and the first node (10) receiving the packets. A method characterized by being equal to time. 5. The method according to claim 4, wherein said delay comprises a processing delay of said second node (20) and a processing delay of said first node (10). how to. 6. The method according to claim 1, wherein the recorded queue size is at least 1 if the recorded queue size is greater than zero.
A method characterized by sending two permits. 7. The central node of a point-to-multipoint communication link.
In 10), the method according to any one of claims 1 to 5 is used. 8. A node (10) of a communication network for receiving information in packets from at least one further node (20), the packet waiting for transmission at said at least one further node (20). Means for storing a queue record representing the number of queues, and means for updating the queue record (11) upon receipt of a queue size value (Rn) from the at least one further node. Record the issuance of a permission (TP) to said at least one further node (20) during a predetermined time, each permission enabling the transfer of at least one packet of information. Means for adjusting an incoming queue size value (Rn) received from said at least one further node (20) based on said recorded authorization value ( 12) A node characterized by the above-mentioned. 9. The node of claim 8, wherein the queue record (11)
) Wherein said means for updating is arranged to utilize the adjusted queue size value (Rn). 10. The node according to claim 8, wherein the delay is equal to a round trip delay between the node (10) and the further node (20). 11. The node according to claim 8, wherein the delay is between transmission of a grant (TP) and reception of the grant by the further node (20). Time and said further node in response to said grant (TP) (20)
The time between the transmission of the packet of information (T) by the node and the reception of the packet by the node (10). 12. In a communication network comprising a central node (10) and several multipoint nodes (20) connected to said central node by a shared medium (100), said central node comprises: Means (11) for storing a queue size record indicating the number of packets waiting to be transmitted at each of the multipoint nodes (20); and a queue size from each of the multipoint nodes (20). Means for updating the queue record (11) upon receiving the value (Rn) of the multipoint node (20) during a predetermined delay. Records the issuance of a permission (TP) that allows the transfer of two information packets and, based on the value of each recorded permission, Node (2
Means (12) for adjusting the value (Rn) of all incoming queue sizes received from (0)
). 13. The communication network according to claim 12, wherein the means for updating the queue record (11) comprises adjusting the corresponding queue size value (Rn).
A) a communication network, wherein the communication network is arranged to utilize 14. A communication network according to claim 13 or claim 14, wherein the delay is the time between sending a grant and receiving the grant by a corresponding multipoint node (20). A communication network, characterized in that it is equal to the sum of the delay between the transmission of a packet by said multipoint node (20) and the reception of said packet by said central node (10).